There have been known various piezoelectric ceramic compositions such as, for example, those comprising PbTiO.sub.3 as a main component, or those containing Pb(Ti,Zr)O.sub.3 as a main component, or their modified solid solutions containing Pb(Mn.sub.1/3 Nb.sub.2/3) and/or Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 as the second or third component. Among them, the compositions of the binary or ternary system containing Pb(Ti,Zr)O.sub.3 as the main component have been used for piezoelectric vibrators, resonators, oscillating elements, ceramic filters, surface acoustic wave filters, pyroelectric elements since they can be improved in piezoelectric and electric characteristics by incorporating additives.
Recently, there have been proposed piezoelectric ceramic compositions of PbTiO.sub.3 with minor substitution of Pb site. Such ceramics have low dielectric constant and higher electromechanical coupling coefficient in thickness vibration mode than that in the radial expansion mode. However, these ceramic compositions of the PbTiO.sub.3 system, more particularly, a ceramic composition consisting of (Pb.sub.1-3x/2 La.sub.x)TiO.sub.3 and an additive of MnO.sub.2, has a serious disadvantage that dielectric breakdown takes place when polarized at high temperature and high voltage. This causes increase in the fraction defective. Also, if such ceramic elements are allowed to stand at high temperatures, it causes deterioration in the piezoelectric characteristics and electric characteristics.